1. Field of the Invention
This invention relates to an improved electrically insulated pipe coupling or union particularly suitable for buried pipes.
2. Description of the Related Art
Metal pipes are vulnerable to electrical corrosion from two different causes. First, galvanic corrosion can result where two dissimilar metals are coupled together. Second, electrical corrosion can result when stray electrical current travels down a metal pipe, which provides the path of least resistance, and thereby causes corrosion where the current leaves the pipe at an anode site. Stray electrical current in metal piping systems is especially prevalent where a piping system such as water pipes is used as an electrical grounding site.
One method of preventing corrosion due to stray electrical current is by insulating the entire metal pipe system thereby preventing the current from ever entering the pipes. However, it has been shown that this method can actually hasten corrosion because the presence of any flaw in the coating will cause the corrosion to be concentrated at the site of the flaw.
Another means of curing the problem of stray current corrosion is to break the circuit along the metal pipe system so that it is no longer the path of least resistance. Electrically insulated pipe couplings or unions are known in the art and are used primarily to electrically insulate sections of metal pipe from each other to minimize corrosion caused by electrolytic action. However, in underground piping applications, insulated connectors can exacerbate the problem because current may travel through the soil around the insulating junction and cause localized corrosion at the point where the current leaves the pipe to travel around the insulated junction.